The present application relates to a bone anchoring device and a bone stabilization device.
A bone anchoring device typically includes a receiving part for receiving a rod-shaped implant element, a bone screw having a thread section for insertion into a vertebral body of a spinal column, and a fixation element for fixating the rod-shaped implant element within the receiving part.
The rod-shaped implant element received by the above bone anchoring device may typically be connected to a further bone anchoring device that is similarly anchored in an adjacent vertebral bone in order to stabilize affected parts of the vertebral column.
One example of a bone stabilization device including two of the above bone anchoring devices and a rod-shaped implant element (in the following also referred to as a “rod element”) is described in document EP 1757243 A1, by the same applicant. Therein, a rod element is disclosed which is composed of a rigid section, a flexible section, a bore formed within the rod element and a core. The core is provided inside the bore and extends through parts of the rigid sections and through the flexible section.
The flexible section may be made of a cylindrical pipe, into which a helical opening extending from the inner bore to the outer surface is formed. The resulting flexible section is characterized by its axial compression or expansion stiffness. The stiffness is achieved by a combination of pitch, web thickness and using biocompatible material's elasticity.
The core may freely slide inside the bore in axial direction at least with regard to one of its ends. Thereby, the free end is guided in a rigid section adjacent to the flexible section. The bending stiffness of the core is bigger than of the flexible section itself. Hence, the bending characteristics of the rod element are determined mainly by the core.
According to EP 1757243 A1, due to the presence of a bore which accommodates the core, the diameter or width of the rod element increases as compared with a common rod element, in which flexible components are not utilized.
The one specific bone anchoring device designed to receive the end section of the rod element is provided with small openings instead of the recesses. The end section of the rod element can be introduced through the openings, whose widths correspond to the reduced width of the end section.
Based on the above, there is a need for an improved bone anchoring device, which provides an enhanced flexibility with regard to a stabilization device including a rod element, and to provide a reliable bone anchoring device which facilitates the implantation of stabilization devices in cases where distance requirements with regard to two adjacently placed bone anchoring devices become very strong, i.e., cases where the mutual distances of those devices are considerably reduced.